1. The Field of the Invention
The present invention relates to the fields of cement compositions and products. More particularly, the present invention relates to improved magnesium oxychloride cement compositions.
2. The Relevant Technology
Cement and cementitious products affect everyone, from the roads we drive on, to the buildings we work in, to the homes we live in. Early principles and applications of cement and cement products were known anciently. The Romans, for example, developed cements and cement products to a high degree of sophistication. Despite centuries of knowledge concerning cements and cement products and despite countless variations of cement compositions, problems still arise while using cements which heretofore have not been adequately solved.
One of the most important uses of cement compositions is in concrete. As used herein, the term “concrete” is broadly defined as a hard strong building material made by mixing an aqueous solution-cementitious powder mixture with a mineral aggregate, often sand and gravel. The cement acts as a glue to bind the aggregate particles together. The setting time and physical properties of concrete vary depending on the cement composition and upon the choice of aggregates.
Concrete is commonly used to construct driveways, sidewalks, floors, and roads (hereinafter referred to generically as “road surfaces”). Concrete road surfaces are usually constructed of Portland cement as a mixture of calcium oxide and water with gravel as an aggregate. Although Portland cement is the industry standard, it is generally slow setting and requires a substantial cure time to reach an acceptable strength. In fact, it has been estimated that Portland cement does not reach full strength for about 100 years.
Sorel cement is another common type of cement. It is a hydraulic cement mixture of magnesium oxide (burnt magnesia) with magnesium chloride together with aggregate materials like sand or crushed stone. Conventional Sorel cement has a poor resistance to water, making it unsuitable for many applications, but is widely used for use in grindstones, tiles, artificial stone (cast stone), cast floors, and even artificial ivory (e.g. for billiard-balls). Magnesia cement floors are credited a high resistance to wear.
Sorel cement is produced by mixing a MgCl2 brine solution with MgO powder. Conventional Sorel cement has a weight ratio 2.5-3.5 parts MgO to one part MgCl2. There is considerable controversy as to what chemical reaction is responsible for the setting reaction of Sorel cement. In the literature, there are several setting reactions presented. The two most prominent are the formation of a 5-phase hydrated magnesium oxychloride product (5Mg(OH)2.MgCl2.8H2O) and a 3-phase hydrated magnesium oxychloride product (3Mg(OH)2.MgCl2.8H2O), each formed according to Equations 1 and 2 below, respectively.5MgO+MgCl2+13H2O→5Mg(OH)2.MgCl2.8H2O  Equation 13MgO+MgCl2+11H2O→3Mg(OH)2.MgCl2.8H2O  Equation 2
Other potential setting reactions discussed include the formation of 2-phase (2Mg(OH)2.MgCl2.4H2O), 9-phase (9Mg(OH)2.MgCl2.5H2O), Mg(OH)2 and MgCl2.6H2O. In addition to the confusion over the setting reaction, there is a lack of knowledge of the kinetics of the setting reaction and the resulting strength of cements made under different conditions. Further details regarding Sorel cements can be found in U.S. Pat. Nos. 5,004,505 and 5,110,361 to Russell I. Alley and George E. Caine, both of which patents are incorporated herein by reference in their entireties.